Method of liquefying natural gas at casing head pressure



NV 5, 1957 w. L. MoRRisoN METHOD OF LIQUEFYING NATURAL GAS AT CASINGHEAD PRESSURE Filed May 7, 1954 INVENTOR, WILLARD L. MORRISON BYATTORNEYS,

PARKER 8r CARTER United States Patent() METHOD OF LIQUEFYING NATURAL GASAT CASING HEAD PRESSURE Wiilard L. Morrison, Lake Forest, lll.,assignor, by mesne assignments, to Constock Liquid Methane Corporation,a corporation of Delaware Application May 7, 1954, Serial No. 428,287

7 Claims. (Cl. 62175) My invention relates to improvements in method andapparatus for liquefying natural gas at casing head pres sure. I proposeto liquefy a portion of the gas entering my apparatus at high pressure,preferably, but not necessarily, directly from the well at casingheading pressure, by reducing it to a temperature at which some of thegas remains liquid at atmospheric pressure. Natural gas is primarilymethane mixed with relatively smaller quantities of water vapor andother gases which have different physical and chemical characteristicsthan methane. Since the gas to which the present invention is primarilydirected is methane, the liquid must be reduced to a temperature notabove approximately -258 F. for that is the temperature at whichmethane, the most intractable of all the elements of natural gas boilsat atmospheric pressure.

In the present invention I propose to cause the gas at high pressure toexpand, thus cooling the gas without doing any mechanical work. Suchcooling will cause condensation as liquid of some of the otherconstituents of natural gas. Such liquids will be removed by drainingafter the reduction in temperature has caused their condensation. Ipropose then toexpand the resultant gas down to a much lower pressureperhaps in the order of atmospheric pressure and as it expands it willbe causedto do mechanical work. The resultant reduction of temperaturedown to approximately. -258 F. will cause some of the methane to becondensed to a liquid which can then be drained oif as a liquid atapproximately -258 F.

Assuming that it is desired to liquefy all of the gas passing throughthe system, the remaining dry gas after the liquid has been removed maybe used to pre-cool the high pressure gas on its way to the expansionturbine or work zone and may thereafter be compressed up to the pressureof the discharge from the expansion chamber, be then mixed with thatdischarge and recirculated through the expansion turbine. This expansionof recirculated gas and of gas prior to recirculation both takes placetogether in the expansion turbine.

My invention is illustrated more or less diagrammatically in theaccompanying drawing which is a diagrammatic layout and flow sheetillustrating my invention.

Like parts are indicated by like characters throughout the specificationand drawing.

1 is the high pressure pipe which conducts natural gas at casing headpressure directly from a gas or oil well or from some other highpressure source to a primary heat exchanger 2 where the temperature ofthe gas is reduced. The Well or other source of supply of gas underpressure is not illustrated since it forms no part of the presentinvention. Since the gas is cooled in the primary heat exchanger somecondensate may result and that is discharged through the drain 3. 4 is apipe leading the high pressure gas past a throttle valve 5 to anysuitable expansion nozzle 6 in the expansion chamber 7 where the gaswithout doing mechanical work expands and is reduced in temperature.This reduction in temperature may result in further condensation of someof the components of the gas which will be discharged through the drain8. The details of the drains 3 and 8 forming no part of the presentinvention are also not illustrated. The cold gas at reduced pressurepasses through the pipe 9, heat exchanger 2 where it cools the gas onits way to the throttle valve. Thence the gas passes through the pipe 10to the precooler 11. The cooled gas from the cooler 11 passes throughthe pipe 12 to the expansion turbine 13 where it expands, does work,driving the generator 14, is cooled and discharged at low pressurethrough the duct 15 to liquid separator 16. Liquid from the separator 16is discharged through the pipe 17 to the liquid reservoir or receiver18. The dry gas, the liquid having been removed, passes from theseparator 16 through the duct 19 to the precooler heat exchanger 11where it cools the gas on the way to the turbine. The gas having passedthrough the precooler is conducted by the pipe 29 to the recyclingcompressor system 21. The details of the compressor are not hereillustrated. Suffice it to say that the gas at turbine exhaust pressurewill be compressed and cooled to the pressure and temperature of the gasin pipe 10. This compressed gas then passes through the pipe 22 to jointhe pipe 10 so that the gas from the expansion chamber is mixed with thegas from the recycling compressor and again passes through the precoolerheat exchanger.

The power to operate the recycling compressor may be provided as at 24.If desired, electrically in part from the generator 14 or any othersuitable source of power. 24 may therefore indicate diagrammatically anelectric motor or a steam turbine or a gas turbine, it being understoodthat while the power generated in the expansion turbine is used tofurnish part of the power to operate the recycling compressor,additional power from any suitable source, preferably by the use of someof the gas itself, must be supplied.

I have illustrated the precooler only diagrammatically. In this case thegas entering from the pipes 10 and 22 is divided and passes through aseries of pipes 25 on its Way to the pipe. Any suitable heat exchange,of course, may be used. The pipe 26 may also return to the system vaporfrom the liquid receiver 18 under control of the valve 27. The pipe 28under control of the valve 29 may bleed oif, if desired, some of the gasbefore it is recycled for other uses of any kind.

I claim:

1. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high presure andtemperature, cooling it, causing the cooled gas to initially expandwithout doing external work but with resultant reduction in temperature,combining the initially expanded gas with stripped gas to be recycled,cooling the combined stream, causing it to expand and do external workwith further reduction in temperature and resultant liquefaction of someof the gas, separating the liquid from the gaseous phase, compressingand cooling the stripped gas to a pressure susbtantially equal to thepressure of the gas after initial expansion, and recycling the strippedgas to combine with said initial expanded gas to form said combinedstream.

2. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, cooling it, causing the cooled gas to initially expandwithout doing external work but with resultant reduction in temperature,combining the initially expanded gas with stripped gas to be recycled,cooling the combined stream, causing it to expand and do external workwith further reduction in temperature and resultant liquefaction of someof the gas,

separating the liquid from the gaseous phase, compressing the strippedgas to a pressure susbtantially equal to the pressure of the gas afterinitial expansion, andtrecycling the stripped gas to combine with saidinitial expanded gas to form said combined stream.

3. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, causing it to initially expand without doing external workbut with resultant reduction in temperature, combining the initiallyexpanded gas with stripped gas to be recycled, cooling the combinedstream, causing it to expand and do external work with further reductionin temperature and resultant liquefaction of some of the gas, separatingthe liquid from the gaseous phase, compressing the stripped gas to apressure substantially equal tothe pressure of the gas after initialexpansion, and recycling the stripped gas to combine with said initialexpanded gas to form said combined stream.

4. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, cooling it, causing the cooled gas to initially expandwithout doing external work but with resultant reduction in temperature,using the expanded cooled gas by heat exchange to cool the gas prior toinitial expansion, combining the initially expanded gas with strippedgas to be recycled, cooling the combined stream, causing it to expandand do external work. with further reduction in temperature andresultant liquefaction of some of the gas, separating the liquid fromthe gaseous phase, compressing and cooling the stripped gas to apressure substantially equal to the pressure of the gas after initialexpansion, and recycling the stripped gas to combine with said initialexpanded 'gas to form said combined stream.

5. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, cooling it, causing the cooled gas to initially expandwithout doing external work but with resultant reduction in temperature,combining the initially expanded gas with stripped gas to be recycled,cooling the combined stream, causing it to expand and do external workwith further reduction in temperature and resultant liquefaction of someof the gas,

separating the liquid from the gaseous phase, using the stripped gas byheat exchange to cool the gas immediately prior to the time that itexpands doing external work, compressing and cooling the stripped gas toa pressure substantially equal to the pressure of the gas after initialexpansion, and recycling the stripped gas to combine with said initialexpanded gas to form said combined stream.

6. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, causing it to initially expand without doing external workbut with resultant reduction in temperature, combining the initiallyexpanded gas with stripped gas to be recycled, cooling the combinedstream, causing it to expand and do external work with further reductionin temperature and resultant liquefaction of some of the gas, separatingthe liquid from the gaseous phase, compressing and cooling the strippedgas to a pressure substantially equal to the pressure of the gas afterinitial expansion and recycling the stripped gas to combine with saidinitial expanded gas to form said combined stream.

7. The method of liquefying gas which consists in supplying it ingaseous phase to a liquefying system at relatively high pressure andtemperature, cooling it, causing the cooled gas to initially expandwithout doing external work but with resultant reduction in temperatureto a point above the temperature of liquefaction of the gas, removingcondensates and combining the initially expanded gas with stripped gasto be recycled, cooling the combined stream, causing it to expand and doexternal work with further reduction in temperature and resultantliquefaction of some of the gas, separating the liquid from the gaseousphase, compressing and cooling the stripped gas to a pressuresubstantially equal to the pressure of the gas after initial expansion,and recycling the stripped gas to combine with said initial expanded gasto form said combined stream.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF LIQUEFYING GAS WHICH CONSISTS IN SUPPLYING IT INGASEOUS PHASE TO A LIQUEFYING SYSTEM AT RELATIVELY HIGH PRESURE ANDTEMPERATURE, COOLING IT, CAUSING THE COOLED GAS TO INITIALLY EXPANDWITHOUT DOING EXTERNAL WORK BUT WITH RESULTANT REDUCTION IN TEMPERATURE,COMBINDING THE INTIALLY EXPANDED GAS WITH STRIPPED GAS TO BE RECYCLED,COOLING THE COMBINED STREAM, CAUSING IT TO EXPAND AND DO EXTERNAL WORKWITH FURTHER REDUCTION IN TEMPERATURE AND RESULTANT LIQUEFACTION OF SOMEOF THE GAS, SEPARATING THE LIQUID FROM THE GASEOUS PHASE, COMPRESSINGAND COOLING THE STRIPPED GAS TO A PRESSURE SUSBTANTIALLY EQUAL TO THEPRESSURE OF THE GAS AFTER INITIAL EXPANSION, AND RECYCLING THE STRIPPEDGAS TO COMBINE WITH SAID INITIAL EXPANDED GAS TO FORM SAID COMBINEDSTREAM.